1. Field of the Invention
The present invention relates to a variable attenuator for use in optical fiber communication and optical network technology, and particularly to a variable attenuator with a rotatable refractor between an input fiber and an output fiber to realize a variable attenuation of optical power.
2. Description of Related Art
A fiber optic attenuator is a passive optical component for reducing optical power propogating in a fiber, and may perform fixed or variable attenuation, which allows high power transmission signals to be processed directly into signal application apparatus. Optical attenuators are widely used in optical transmission systems and optical networks.
Means for providing fixed attenuation are well known in the art, which generally utilize a medium of fixed optical density disposed between a signal input fiber and a signal output fiber. These media can comprise isolated material placed between the signal carrying fibers, or can comprise a coating upon the terminal end of at least one of the signal carrying fibers.
In the past, variable attenuators have reduced signal levels by transmitting such signals through partially opaque optical filters, by obstructing a section of the signal with attenuation filter segments, by varying the orientation between signal input and output fibers, or by diminishing signal strength via reflecting from partially light absorbent elements.
For example, U.S. Pat. No. 4,591,231 describes an optical attenuator containing a disk having a plurality of openings with fixed, neutral density filters of differing optical density contained therein. By rotating the disk, a fixed density filter of a desired opacity can be introduced into the signal path, thereby attenuating a portion of the signal. Although effective for reducing signal strength, such a system is limited in that attenuation levels vary in a step-wise rather than a continuous manner.
U.S. Pat. No. 4,938,989 discloses another variable attenuator. As shown in FIG. 6, such attenuator 100 comprises a housing 150 containing a first optical fiber connector 140, a first optical lens 160, a first connecting optical fiber 180, a second optical lens 200 separated from the first optical lens 160 by an optical coupling region, a second optical fiber connector 220, a second connecting optical fiber 240, an optical filter 260 and a reciprocating means 280. The optical filter 260 is a flexible film having an optical density gradient varying along its length, which is mounted in an orientation substantially orthogonal to the optical axis within the optical coupling space between each of lenses 160 and 200. The filter 260 is operably connected to the reciprocating means 280 to vary the vertical position of the filter 260. As the density of the filter 260 is a gradient along its length, such vertical movement serves to provide areas or regions of differing optical density that transmits and absorbs differing amounts of light, thereby providing a continuously variable filter means between the lenses 160 and 200. In this application, the design and the manufacture of the filter are difficult and complex, making the cost of the attenuator high.
It is desirable to provide a variable attenuator for overcoming the above problems.
An object of the present invention is to provide an improved variable attenuator having a refractor that is used for reducing optical transmission signals in a continuous manner.
Another object of the present invention is to provide a simple and low-cost variable attenuator that is easy to operate.
To achieve the above objects, in accordance with the present invention, a variable optical attenuator of the present invention comprises a holder, a rotatable mechanism, a refractor, an input port and an output port. The input port and the output port are engaged with corresponding upright beams of the holder, which hold the input port and the output port in alignment with each other. The refractor is mounted on the rotatable mechanism by adhering to or soldering on the groove of the rotatable mechanism, wherein the rotatable mechanism mates with the through hole of the holder to make the center of the refractor and the optical axis of the input and output collimators of the input and output ports in line.